Improve subs for Derivative.

Perform substitutions if derivative variables are in a different, but
equivalent order and perform substitutions for subderivatives.
Add additional tests for Derivative subs method.
Solutions for quadratic ternary forms implemented
Descent method improved
Removed '== True' part from the assertions
Adding Dynkin diagram functionality
Holzer reduction implemented
Holzer reduction
merging with master
Code cleanup
Code clean up
Removed whitespaces
Attempt to fix test failure
Updating some things
Solution method improved
An Attempt to fix build failures
Fixing some errors
Attempt to fix build errors
Attempt to fix build errors
Attempt to fix build failures